1. Field of the Invention
The present invention relates to a centrifuge equipped with a balancer, particularly, to a centrifuge equipped with the balancer which contains balls and liquid to reduce force and moment generated due to the weight imbalance among samples loaded a rotor and makes the rotor rotate more steadily. The balancer reduces vibration of the centrifuge, prolongs lifetime of the centrifuge and the rotor, and enhances the efficiency of the centrifugal separation.
2. Description of the Related Art
To accelerate settling of materials melt in fluid or suspended materials contained in a suspension, centrifugal force is used instead of gravity. This process is referred as centrifugal separation.
A centrifuge used for the centrifugal separation is an apparatus using a phenomenon that high density particles move to the edge and low density particles concentrate on the center in a suspension due to the centrifugal force. An example of a structure of the centrifuge is shown in FIGS. 1a and 1b. 
As shown in FIGS. 1a and 1b, a centrifuge is configured with a buffer member 30 such as the anti-vibration rubber and damper set up on first supporting plate 15 formed in the inner side of a case 10 of the centrifuge and a bracket or second supporting plate 35 installed on the buffer member 30.
Also, a configuration of the centrifuge includes a motor 50 beneath the bracket or the second supporting plate 35 and a rotor 200 or 200a on a shaft 40 protruded from the motor 50.
The centrifuge uses different types of rotors according to the usage and there are two general types of rotors such that a swing-out rotor 200a, which rotates perpendicularly to the shaft of the motor, and a fixed-angle rotor 200 which has a space rotating with fixed angle. The fixed-angle rotor 200 may include a plurality of chambers 60.
The motor 50 in the centrifuge rotates at high speed and gives a big strong centrifugal force to samples within bottles or test tubes loaded into the swing-out rotor or the fixed-angle rotor. Therefore, the centrifuge separates the materials contained within the samples by the difference of the centrifugal forces due to the difference of densities between the materials.
A big centrifugal force has to be given to the samples for the separation of the materials within the samples. High speed rotation of the rotor is generally required in order to generate a big centrifugal force to the samples and particularly vibration should not be generated by the high speed rotation of the rotor.
However, during the high speed rotation of the centrifuge, vibration is generated by a bending motion of the shaft of the motor, a whirling motion due to the weight imbalance of the rotor, and influences by the other external factors. And the whirling motion by the weight imbalance of the rotor is the main factor among these reasons of the vibration.
Accordingly, in the centrifuge without a balancer, an operator measures independently the weight of each sample in advance before the centrifugal separation operation in order to remove the weight imbalance of the rotor generated due to the difference in the number of samples loaded into the rotor or due to the difference in the weight of each sample. Therefore, there has been an inconvenience that an operator should perform the centrifugal separation that after removing the weight difference between the opposite-side samples. If the weight imbalance between the opposite-side samples exists, materials within the samples are not separated due to the vibration generated during the centrifugal separation process. Although materials might be separated, the materials might be mixed again by the vibration.
Furthermore, during the centrifugal separation process, some noise may be generated by the vibration.
In the centrifuge, there has been a problem that a force or a moment is generated due to the weight imbalance among samples and it causes a disorder of the centrifuge itself.
To resolve the problem of the noise and the vibration generated during the centrifugal separation process, the buffer member such as damper and rubber may be included. But the buffer member still has a problem that noise and vibration are not absorbed enough.
Therefore, to resolve the problems of noise and vibration generated due to the weight imbalance among samples, the centrifuge equipped with a balancer including balls has been proposed.
The ball balancer (hereinafter, it is referred as Conventional Technology 1) shown in FIG. 2a contains a plurality of balls 420 in the case 400 forming the balancing space 410 shaped as a circular ring and has an axis hole 430 at the center to fix the shaft of the motor.
Thus, the ball balancer includes balls 420 to fill some portion of the balancing space 410 formed inside of the case 400 and has the advantage that if the rotational speed of the motor (not illustrated) is above the resonance speed then rotation is stable because the balls move to the opposite side of the weight imbalance amount and the rotor (not illustrated) is balanced.
But there is a disadvantage that if the rotational speed of the rotor is below the resonance speed then the rotor is more unstable because the balls 420 rather move to the side where the weight imbalance exists.
To resolve the problem of the ball balancer of Conventional Technology 1, the ball balancer shown in FIG. 2b (hereafter, it is referred as Conventional Technology 2) has been proposed.
The ball balancer has the balancing space 410a formed to be inclined from the center of a case 400a having a hollow to the edge and includes balls 420a which fill up the groove part of the edge of the balancing space 410a formed within the case 400a. 
The ball balancer has an axis hole 430a. 
The ball balancer may prevent the unstable rotation occurred at the time of low-speed rotation under the resonance speed because the balls 420a locate near the center of rotation at that time.
Furthermore, if the motor rotates at high speed above the resonance speed then balls are floated by the centrifugal force and move to the opposite side to compensate the weight imbalance amount. Thus, the ball balancer has an advantage of vibration and noise reduction because the rotor rotates at a stable state.
However, in case of the ball balancer shown in FIG. 2b, if the rotational speed of the motor increases over the resonance speed starting from the initial low speed then it takes some time for the balls to move to the opposite side to compensate weight imbalance amount. Therefore, the ball balancer has a disadvantage that it does not have sufficient effect of vibration attenuation because vibration is created at this moment.